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Post by togermano on Jun 23, 2011 9:56:43 GMT -6
I have an antenna question... Is it possible to use my cb antenna that I alreeady have on my roof or is an fm antenna different? I would also need a converter to convert the connection plugin type
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Post by Kage on Jun 23, 2011 12:40:59 GMT -6
No you can not use a CB antenna as is because they are designed to operate at 26-27MHz. Your FM transmitter runs at a much higher frequency and if you were to connect your CB antenna to it I can almost guarantee you that the transmitter will overheat and kill itself off quickly.
Antennas must be designed for the frequency of operation that they are to be used for when it comes to transmission.
There's a very real science behind antenna design. Using an antenna not designed for the proper use will either turn your 10 watt transmitter into a permanent paper weight or only get your signal out a few yards if you're lucky.
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Post by togermano on Jun 23, 2011 13:25:18 GMT -6
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Post by Ozone Express Radio on Jun 25, 2011 21:47:59 GMT -6
The Chinese transmitters are OK for the price. I've had one for a while, but here are some things I've found:
They do have some weird harmonics and spurs when operated by themselves. Even as advertised with a filter built-in, they still aren't well filtered.
Channel 6 TV will be affected by this transmitter. If you still have an analog CH6 in your area, it may interfere with the sound.
The antennas that are supplied with these Chinese transmitters are junk. Buy a decent antenna and SWR meter and tune it properly and you'll do pretty good.
The coax they supply is also garbage. Buy something decent like LMR400 or the like.
Invest in a decent LPF. You will be less likely to interfere with any other communications, and have the peace of mind knowing you are putting out a clean signal.
Keep a couple of output MOSFET transistors on hand. These units don't like mismatches with the antenna. They will fry the output transistors easily. Especially if you operate them with the top cover off for a few minutes. Ask me how I know. ;D
Don't use the laptop style power supply that comes with them. They are dirty power and tend to fluctuate a lot. A regulated power supply is recommended and will give better results.
Other than that, they sound pretty decent, and put out a respectable signal. My 20 Watter is reaching out to around 10 miles or so.
Of course, all this said, you will really be buying just the transmitter and tossing all the stuff they send along if you buy a package deal.
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Post by RFBurns on Jul 2, 2011 10:24:05 GMT -6
As I pointed out in another thread, those Chinese transmitters require a bit of tuning on their LPF and perhaps a bit of tweaking in the inter-stages prior to the final. They are pre-set for the middle of the band as far as the filter goes. Adding a 2nd LPF is obviously the way to go no matter what with ANY transmitter.
Fully agree...the tiny 1/4 wave GP and coax is junk...as is a few of the power supplies that come with them. Now as to the power supplies, that depends on which one you end up with. There are 4 different types that are used, the best being their hefty supply to power the 15 and 25 watt tx's.
Any switching power supply produces noise no matter what, inductively and in the supply rails. Ever wonder why the supply rail inside your laptops and desktops have up to 10 filter caps in parallel on all the voltage rails as well as chokes? Well there ya go.
Thing to keep in mind is any transmitter no matter its make or era can produce all the garbage just like these units from China if they are not tuned right or loaded right.
When the basics are ignored for the sake of package deals across the other pond, well obviously the end results will be less than enthusiastic. Don't blame the device when its owner ignores all other aspects of setting up a proper facility and adhering to good engineering practices. In other words, do what is necessary as it would be with a Harris or Continental or Broadcast Electronics transmitter and set them up the way they should be.
Just throwing a signal on the air is not good enough, unless the intent is to jam the spectrum with junk..which at that point your better served setting up a large spark gap transmitter.
Side note(my opinion only and does not reflect this forum or other member's point of view)...those "other" communities...I have found them to be nothing more than a gathering of stuffy smoke filled rooms of status quo's all retired with nothing better to do. Too much time on their hands instead of touring the countryside in RV's or cruise ships. No imagination, no exploration, and no stepping out of line when it comes to creativity. Toe the line as it were. BAH! Funny, but the last time I checked the dictionary, the word "hobby" meant just that, and it implies to experiment, to learn, to grow...and venture beyond the edge of the piece of paper and numbers on a slide rule. Moral to the story....go past the boundaries and discover all kinds of neat ways to do things besides the ho hum drum method that cannot be improved upon unless one does venture beyond the leash.
Peace.
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Post by RFBurns on Jul 2, 2011 10:29:24 GMT -6
I have an antenna question... Is it possible to use my cb antenna that I alreeady have on my roof or is an fm antenna different? I would also need a converter to convert the connection plugin type To use a CB antenna, you would have to trim the elements down to the frequency of operation, which if you trimmed them to equate to a 5/8 wave GP, it would not need to be trimmed too much. Attach slightly smaller elements to slide inside the antenna's elements and use hose clamps to secure. Slide these elements until you achieve resonance (lowest VSWR) and lock them down with the hose clamps. Take ordinary clear silicone and coat those areas to prevent corrosion and the like. It can be done....I have done it and still have that modified CB antenna in use today after 25 years. Peace. |
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Post by alcyone on Jul 16, 2011 12:41:58 GMT -6
Did you ever buy this transmitter and if so what do you think about it? I just got one and am waiting for it to be delivered. I was looking for a transmitter where I could use my existing ground plane antenna, but scale the power back enough to keep it legal. |
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Post by Ozone Express Radio on Jul 16, 2011 21:11:28 GMT -6
If you are planning on using a 10 W transmitter and a ground plane, I am not sure how you plan on making it legal.  That is unless you have a license. |
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Post by RFBurns on Jul 17, 2011 22:52:37 GMT -6
Well hopefully he got one that can be switched in power to the 1 watt level and then run it into an attenuator (hefty) to obtain that 250uv/m@3m legal limit.
Peace!
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Post by Ozone Express Radio on Jul 18, 2011 7:58:12 GMT -6
With 15 watts through a Comet GP set at 35 feet, I am easily reaching 6 miles in the flat direction around my location. The hilly area I still have a hard time penetrating, but get a respectable 3 miles or more depending on weather and other factors. When I fire up the 175W unit, the coverage gets a tad further.....  |
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Post by alcyone on Jul 23, 2011 17:31:04 GMT -6
The transmitter is power adjustable down to 1 mw. Going straight to the ground plane the signal only went a couple houses down the street.
I was planning to turn the RF output down and use an attenuator which I have. However, if I scale the power back the transmitter heats up to the point where it feels like it'll burn itself out.
I'm not very happy with this unit. I think it's cheap and leaves much to be desired in terms of build quality and sound quality. For right now, I'm using a self made dummy load which contains the signal enough.
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Post by terrydec on Jul 24, 2011 11:39:55 GMT -6
I've shut down, but I used a 15 watt Chinese transmitter with a quarter plane tuned to my frequency, (there's a web site for this.) It was mounted on a chimney about 75' off the ground. The feed line was some super-duper RG6. The feed line was exactly 6 times the antenna height, which gave an SWR of between 2:1or 3:1. The transmitter operated perfectly for almost a year for 12 hours a day It had great stereo separation and frequency response. I had a friend check for sideband radiation and it was practically null. I asked all of my neighbors if they were hearing music on their phone, TV, etc. Every house is wired and cell phones work in the ghz range so there was no interference. And amazingly no airplanes fell out of the sky. If there had been any complaints I'm sure I would have heard. By the way, don't listen to a bunch of scare stories about going to jail if you are caught. Just turn the transmitter off and throw it away. The only fines or forfeitures are leveled against people who continually ignore warnings, like Stephen Dunifer. (P.S. Don't buy from him, he is VERY unreliable- that's just my experience) or purposefully cause interference. You know who gets fines and forfeitures? Licensed radio and TV stations that refuse to keep EAS logs, don't paint antennas and stuff- Here are links to the FCC notics of violation and notice of action transition.fcc.gov/eb/FieldNotices/ transition.fcc.gov/eb/rfo/ActAct.htmlThe interesting part is that no one operating without a license on the NOA appears on the NOL. I LOVED having my station a turned it off just because it was time. I'd moved on to other stuff. I believe that there is nothing worse that being ordinary. |
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Post by Ozone Express Radio on Jul 27, 2011 21:09:44 GMT -6
However, if I scale the power back the transmitter heats up to the point where it feels like it'll burn itself out. I'm not very happy with this unit. I think it's cheap and leaves much to be desired in terms of build quality and sound quality. For right now, I'm using a self made dummy load which contains the signal enough. Those Chinese units have a thermal protection built into them that actually works (ask me how I know) and I never lost an output transistor to heat. I did zap a couple because of bad mismatches with antennas. How hot did yours get? I've not pointed my infrared thermometer at the case when it was running, but my 20 Watter is pretty cool to the touch with the fan running while broadcasting, although the heat sink inside is hot enough to burn you and my 1mW unit is cool as a cucumber when running and it isn't fan cooled. I'd be checking the SWR and see what's going on. |
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Post by RFBurns on Jul 28, 2011 6:23:18 GMT -6
The transmitter is power adjustable down to 1 mw. Going straight to the ground plane the signal only went a couple houses down the street. Odd. Even at 1mW to a ground plane 10 feet into the air should get you a couple of blocks. I know, I have a setup using the el-cheapo 1/4 ground plane on a 8 foot fence pole fed with the 1mW unit and surrounded by mobile homes, the signal reaches 3 blocks on a bad day, up to 5 on a good day after a rain. This is my "fall back" setup for those "don't feel right" days. I suspect you may have a VSWR issue. Even at 1mW a high VSWR will kill that flea signal just as bad as a high VSWR would kill a 1KW signal. I was planning to turn the RF output down and use an attenuator which I have. However, if I scale the power back the transmitter heats up to the point where it feels like it'll burn itself out. How are you tapping the power after the attenuator, and is the attenuator a "non-inductive" load? The transmitter should operate at normal temperature even running through an attenuator, it is the attenuator that should be getting a bit warm. However with an attenuator inline or not, if there is a high VSWR on the feedline and/or antenna itself, no doubt that will make the TX run hot. I'm not very happy with this unit. I think it's cheap and leaves much to be desired in terms of build quality and sound quality. For right now, I'm using a self made dummy load which contains the signal enough. If the load, dummy or antenna, is a non-inductive 50 ohm load, or a well tuned antenna, the unit should run fine and sound good. A high VSWR will not only kill the signal coverage, but will also dampen the carrier bandwidth as well as shunt the channel separation by feeding all that back into the transmitter output, then into the driver stages and into the modulator and stereo generation circuits...be it a package IC or separate circuits. Imagine if we could hear VSWR, much like how we can hear feedback from a microphone too close to a loudspeaker. What happens to sound when feedback is present? It gets "shunted" and overtaken by the feedback. Same happens to RF with a high VSWR and the audio also becomes overtaken by the VSWR, causing it to sound muddy or weak, along with a sweating transmitter getting too hot. As OER suggested, get a SWR meter and check things. The Workman SWR -3P is a good meter and can be found in abundance on ebay for around 25 mulas. The finals in those Chinese units have internal thermal and short protection, though the short protection is "short" lived, meaning too long of a short or high VSWR will blow out the final. Too bad they did not incorporate an auto-shut down or crowbar circuit to dampen the power level in the event of a high VSWR. Many operators believe that they can overcome a VSWR issue by simply cranking up the power to compensate, but all that increased RF power is doing nothing but increasing the VSWR ratio, and in turn dumping the increased reflected RF back into the output....POOF! (who let the smoke out...POOF...POOF POOF POOF!) An improper matched antenna and coax can also cause increased spectrum garbage which will rob your transmitter of power output and scatter that power across the spectrum at the harmonic points. With a proper match, you can crank up the power and the VSWR ratio should be the same, plus or minus a point or two in proportion to the power output. In any case, when properly tuned, the antenna and coax should present a near perfect load match. Taking the time to obtain that "as close as possible" match is well worth the effort in both signal coverage and sound quality. Peace! |
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Post by alcyone on Jul 28, 2011 21:22:06 GMT -6
Those Chinese units have a thermal protection built into them that actually works (ask me how I know) and I never lost an output transistor to heat. I did zap a couple because of bad mismatches with antennas. How hot did yours get? I've not pointed my infrared thermometer at the case when it was running, but my 20 Watter is pretty cool to the touch with the fan running while broadcasting, although the heat sink inside is hot enough to burn you and my 1mW unit is cool as a cucumber when running and it isn't fan cooled. I'd be checking the SWR and see what's going on. Strangely enough I broadcasted into a wire wound resistor dummy load with an HLLY 5 watt for years (I was told this was like transmitting into open ended coax). The transmitter never burned up. They actually sent me another unit by mistake, which arrived today.  So I guess if burn this one up I have another one. The heat is only an issue when the power is scaled back. Otherwise it remains cool. |
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That is unless you have a license.
So I guess if burn this one up I have another one.